Millionaires' top 5 investing mistakes

Millionaires make some of the same investment mistakes as everyone else—it's just that their mistakes can cost more.

A new survey of millionaire investors around the world found five mistakes that are most common among millionaires.

The most widespread: failure to diversify. While a concentrated position in a single asset or industry can certainly help make someone rich, it's a recipe for disaster when trying to invest or preserve wealth.

The study by deVere Group, a global independent financial consultancy, surveyed 880 investors around the world with investible assets of $1.5 million or more. Of that, more than 100 were in the U.S.

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When asked their number one investing mistake, 23 percent of those surveyed cited a failure to adequately diversify their portfolio.

Coming in a close second, at 22 percent, was "investing without a plan." Fully 20 percent said their biggest mistake was "making emotional decisions," and 16 percent said "failing to regularly review the portfolio." The number five mistake is "focusing too heavily on the history of an investment's returns."